The diagnosis of acute cholecystitis remains a clinical problem. The finding of a normal oral cholecystogram makes the disease highly unlikely, but failure to visualize the gallbladder may be due to other causes. Intravenous cholangiography is of considerable value, but may have a false positive rate of 15 to 50%. In an effort to overcome this problem, we have devised a procedure for reliable gamma camera imaging of the gallbladder after intravenous administration of a radiolabeled bile salt analog. Our preliminary work in dogs and humans suggests that after emptying the gallbladder by the administration of cholecystokinin, we can reliably visualize it with 99mTc dihydrothioctic acid. With computer assistance we can quantify the rate of accumulation of activity and subsequently measure the emptying of the gallbladder after a second dose of cholecystokinin. In pilot studies so far, we have succeeded in identifying all patients with cystic duct obstruction due to acute cholecystitis. We propose to: 1) perform animal experiments to define optimum conditions for performing the test 2) assess the effects of drugs in animals that a patient may be receiving, and 3) define in humans the value of the test in the differential diagnosis of acute cholecystitis.